Fig. 1. Schematic diagram of optical path in FPI

Fig. 2. Schematic diagram of filtering light by FPI

Fig. 3. Interference peaks at different central wavelengths of FPI under different driving voltages

Fig. 4. Operation flow chart of system

Fig. 5. Measured lamp spectrum and absorption spectra. (a) Measured lamp spectrum and absorption spectrum; (b) absorption spectrum with slight fluctuation

Fig. 6. Measured dark spectrum

Fig. 7. τCO2 obtained after processing the measured absorption spectrum

Fig. 8. Structural diagram of gas measuring instrument based on tunable FPI sensor

Fig. 9. Lamp spectra at different modulation frequencies

Fig. 10. Dark spectra at modulation frequencies of 10 Hz and 20 Hz

Fig. 11. Non-sequential simulation of optical path by ZEMAX. (a) Magnification of detector end; (b) magnification of lens end

Fig. 12. Principle block diagram of system

Fig. 13. Physical diagram of system

Fig. 14. Inversion examples of spectra for CO₂ with concentration of 9.9×10^-5. (a) Absorption spectrum and fitted spectrum; (b) residual spectrum after fitting

Fig. 15. Changes of lamp spectra before and after introduction of nitrogen

Fig. 16. Time series of concentrations of CO₂

Fig. 17. Frequency distributions of concentrations of CO₂

Fig. 18. Linear fitting between measured value after iterative inversion and nominal value

Fig. 19. Concentration distributions of CO₂ at different dates in 2021 measured by outfield experiment

Fig. 20. Concentration distributions of CO₂ at different times in 2021